1. Field
This invention relates to detection systems and circuits. Specifically it provides for a system which detects a particular event or circumstance and causes the occurrence of a desired operation related to such detection. More specifically, it provides a system to detect the deroping of a cable from the grooved wheels on a cable tower of a chair lift system and indicate the location of the deroping and shut down the chair lift system upon deroping.
2. State of the Art
Detection systems such as those described in U.S. Pat. No. 2,871,466 (Vassil, et al.); U.S. Pat. No. 3,412,391 (Ward) and U.S. Pat. No. 3,594,740 (Comeau) typically employ voltage sources to supply an electrical signal having fixed voltage level to its sensing circuiry. The incidence of a stimulus (that which is to be detected) does not affect that voltage. Various electrical parameters (e.g., current) in the detecting circuitry are varied upon incidence of the stimulus and sensed to effect the operation desired (e.g., alarm).
Reliance on electrical parameters in the sensing circuitry suggests that such systems are limited to environments in which the ambient temperature is relatively constant absent the use of costly components and more components to adapt the system to a variable environment. Further, the use of a fixed voltage supply limits the amount of wiring between the voltage supply and the sensing circuity and in turn geographical distance therebetween because of the internal resistance of the wiring and the voltage drop experienced in the wiring. Further, such systems require the use of electrical components which differ from detector (sensing circuitry) to detector so that one detector is not interchangeable with another.
Chair lift systems of the type used to transport skiers to the top of a hill or mountain are well known. They are comprised of a plurality of intermediate towers to support a cable to which the chairs are attached. Each tower includes a cable transport and support device which is typically a grooved rotatable wheel, the cable fitting or riding in the groove. Should the cable jump out of the groove (deroping), a substantial hazard to people in the chairs would arise if the chair system movement is not immediately stopped.
Typical chair lift systems have a movable counterbalance weight to tension the cable with a safety system associated therewith to shut down the system when excessive counterbalance weight movement is detected. Upon deroping such movement might or might not occur, or if it occurs, it might occur too late in time to prevent harm to the people in the chairs.